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SubjectRe: [PATCH v10 03/18] rtc: sun6i: Fix time overflow handling
On Fri, 11 Feb 2022 12:26:28 +0000
Andre Przywara <andre.przywara@arm.com> wrote:

Hi Alessandro, Alexandre,

I was wondering if you would consider taking this (as a fix)?
This (time_gap > U32_MAX) comparison looks flawed by design, and we should
use time_t these days anyway.

Also, do you have an opinion on the other RTC patches? The linear day
patch (v10 04/18)[1] and the broken-down alarm registers (v10 05/18)[2]
were on the list for a while now and are needed by other SoCs as well
(R329[3] and the RISC-V D1).

Cheers,
Andre
[1] https://lore.kernel.org/linux-arm-kernel/20220211122643.1343315-5-andre.przywara@arm.com/
[2] https://lore.kernel.org/linux-arm-kernel/20220211122643.1343315-6-andre.przywara@arm.com/
[3] https://lore.kernel.org/linux-arm-kernel/20210802062212.73220-3-icenowy@sipeed.com/

> Using "unsigned long" for UNIX timestamps is never a good idea, and
> comparing the value of such a variable against U32_MAX does not do
> anything useful on 32-bit systems.
>
> Use the proper time64_t type when dealing with timestamps, and avoid
> cutting down the time range unnecessarily. This also fixes the flawed
> check for the alarm time being too far into the future.
>
> The check for this condition is actually somewhat theoretical, as the
> RTC counts till 2033 only anyways, and 2^32 seconds from now is not
> before the year 2157 - at which point I hope nobody will be using this
> hardware anymore.
>
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>
> ---
> drivers/rtc/rtc-sun6i.c | 14 +++++---------
> 1 file changed, 5 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/rtc/rtc-sun6i.c b/drivers/rtc/rtc-sun6i.c
> index 35b34d14a1db..dc3ae851841c 100644
> --- a/drivers/rtc/rtc-sun6i.c
> +++ b/drivers/rtc/rtc-sun6i.c
> @@ -139,7 +139,7 @@ struct sun6i_rtc_dev {
> const struct sun6i_rtc_clk_data *data;
> void __iomem *base;
> int irq;
> - unsigned long alarm;
> + time64_t alarm;
>
> struct clk_hw hw;
> struct clk_hw *int_osc;
> @@ -511,10 +511,8 @@ static int sun6i_rtc_setalarm(struct device *dev,
> struct rtc_wkalrm *wkalrm) struct sun6i_rtc_dev *chip =
> dev_get_drvdata(dev); struct rtc_time *alrm_tm = &wkalrm->time;
> struct rtc_time tm_now;
> - unsigned long time_now = 0;
> - unsigned long time_set = 0;
> - unsigned long time_gap = 0;
> - int ret = 0;
> + time64_t time_now, time_set;
> + int ret;
>
> ret = sun6i_rtc_gettime(dev, &tm_now);
> if (ret < 0) {
> @@ -529,9 +527,7 @@ static int sun6i_rtc_setalarm(struct device *dev,
> struct rtc_wkalrm *wkalrm) return -EINVAL;
> }
>
> - time_gap = time_set - time_now;
> -
> - if (time_gap > U32_MAX) {
> + if ((time_set - time_now) > U32_MAX) {
> dev_err(dev, "Date too far in the future\n");
> return -EINVAL;
> }
> @@ -540,7 +536,7 @@ static int sun6i_rtc_setalarm(struct device *dev,
> struct rtc_wkalrm *wkalrm) writel(0, chip->base + SUN6I_ALRM_COUNTER);
> usleep_range(100, 300);
>
> - writel(time_gap, chip->base + SUN6I_ALRM_COUNTER);
> + writel(time_set - time_now, chip->base + SUN6I_ALRM_COUNTER);
> chip->alarm = time_set;
>
> sun6i_rtc_setaie(wkalrm->enabled, chip);

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